Dear M. Rowlands
Thanks for using Microsoft products and posting in the Community.
Based on your description, it should actually be pretty clear.
Ultimately, your question is still how to configure Blueyonder mailbox on Outlook.
I can understand that you want to use Blueyonder mailbox on Outlook as soon as possible.
According to the error report you posted before, my suggestion is that you need to confirm whether the data is migrated to Outlook or not, if it is migrated over, what is the new mailbox after it is migrated over? If it is not migrated, but just cooperated with Microsoft, is the account protocol type of Blueyonder mailbox Exchange protocol? For these questions, you need to contact the mailbox administrator of Blueyonder mailbox.
If it's just Exchange protocol, the configuration error message posted earlier, it's obvious that you chose the wrong protocol, that's why I'll confirm with you earlier if it's imap, pop, Exchange protocol, when you configure the mailbox, you need to choose the correct protocol to configure it successfully.
If the data is migrated, then the migrated new Outlook mailbox, your mother should know, if not you can also check the mailbox by contacting the Blueyonder mailbox mailbox administrator, these are the privacy of the enterprise, Microsoft does not have the authority to check.
Best wishes
Clark | Microsoft Community Support Specialist